ReaderTextCellParallel (SystemDS 2.0.0 API)

```
public class ReaderTextCellParallel
extends ReaderTextCell
```
Parallel version of ReaderTextCell.java. To summarize, we create read tasks per split and use a fixed-size thread pool, to executed these tasks. If the target matrix is dense, the inserts are done lock-free. If the matrix is sparse, we use a buffer to collect unordered input cells, lock the the target sparse matrix once, and append all buffered values. Note MatrixMarket: 1) For matrix market files each read task probes for comments until it finds data because for very small tasks or large comments, any split might encounter % or %%. Hence, the parallel reader does not do the validity check for. 2) In extreme scenarios, the last comment might be in one split, and the following meta data in the subsequent split. This would create incorrect results or errors. However, this scenario is extremely unlikely (num threads > num lines if 1 comment line) and hence ignored similar to our parallel MR setting (but there we have a 128MB guarantee). 3) However, we use MIN_FILESIZE_MM (8KB) to give guarantees for the common case of small headers in order the issue described in (2).

Nested Classes
Modifier and Type	Class and Description
`static class`	`ReaderTextCellParallel.CellBuffer` Useful class for buffering unordered cells before locking target onces and appending all buffered cells.
`static class`	`ReaderTextCellParallel.CountNnzTask`
`static class`	`ReaderTextCellParallel.ReadTask`

Constructors
Constructor and Description
`ReaderTextCellParallel(Types.FileFormat fmt)`

Method Summary
- Methods inherited from class org.apache.sysds.runtime.io.ReaderTextCell
  readMatrixFromHDFS, readMatrixFromInputStream
- Methods inherited from class java.lang.Object
  equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

public ReaderTextCellParallel(Types.FileFormat fmt)

Class ReaderTextCellParallel